1. Field of the Invention
The invention relates to automatic swimming pool cover systems, and in particular, to hydraulic drive systems for rotating the cable reels and cover drum for extending and retracting pool covers back an forth across a swimming pool.
2. Description of the Prior Art
Automatic swimming pool cover systems typically include a flexible vinyl fabric sized so that most of it floats on the surface of the pool water. The pool water acts as a low friction surface significantly reducing the amount of force required to move the cover across the pool. The front edge of the cover is secured to a rigid boom spanning the width of the pool for holding the front edge of the cover above the water as it is drawn back and forth across the pool.
To draw the cover across the pool, a cable, typically a Dacron line, is incorporated into and forms a beaded tape which is sewn or attached to the side edges of the pool cover. The beaded tape in turn is captured and slides within a "C" channel of an extruded aluminum track. The track is secured either to the pool deck or the the underside of an overhanging coping along the sides of the swimming pool. The cables extending from the beaded tape sections of the cover are trained around pulleys at the distal ends of the tracks and return in a parallel "C" channel to the drive mechanism where they wind around cable take-up reels.
To uncover the pool, the drive mechanism rotates a cover drum mounted at one end of the pool winding the pool cover around its periphery and unwinding the cables from around the take-up reels. To cover the pool the drive mechanism rotatably drives the cable take-up reels winding up the cables to pull the cover across the pool unwinding the cover from around the cover drum.
The rate at which the pool cover unwinds from and winds onto the cover drum varies depending on the diameter of the roll of the cover still wound around the drum, i.e., the rate is greatest when most of the cover is wound around the drum (largest diameter) and least when the cover is practically unwound from the drum (least diameter). The same phenomenon occurs as the cables wind onto and unwind from the cable reels. It should be appreciated that the cables wind onto the cable reels at the highest rate when the cover unwinds from the cover drum at its lowest rate and visa-versa
In systems where the cable take-up reels and the cover drum rotate together on the same axle, but oppositely wind/unwind the cables and cover respectively, a spring is utilized as a tensioning take-up mechanism to compensate for the different and varying rates at which the cables and pool cover wind and unwind from the respective reels and drum during the opening and closing cycles. The spring mechanism lengthens and shortens the cable path as the cover is drawn back and forth across the pool taking up and yielding slack in the respective cables as necessary to compensate for the differences in the winding and unwinding rates of the reels and drum. [See U.S. Pat. Nos. 3,747,132 & 3,982,286, Foster].
In spring tensioning take-up systems of the type described by Foster, and later floating spring tensioning take-up systems of the type pioneered by Last, the applicant herein, the tensioning of the cables by the spring(s) assures that the cover, and especially its beaded edges curling around the ends of the drum, wind tightly and uniformly without substantial bias around the cover drum as the cover is retracted from across the pool. However, there is an upper limit beyond which the tensioning/compensating spring of such single axle systems can not compensate for the differential in winding rates of the cover and cables. [See U.S. Pat. No. 3,982,286, Foster, Col. 5, 1.36-Col. 6, 1.4. See also related U.S. Pat. No. 4,939,798].
In other systems, a clutching mechanism is typically utilized to decouple the rotation of the cable reels from that of the cover drum as it is rotatably driven to wind the cover onto the drum uncovering the pool, and to decouple the rotation of the cover drum from that of the cable reels as they are rotatably driven to draw the cover across the pool. Typically, in such systems, the cable reels are allowed to free wheel when the cover drum is rotatably driven and conversely, the cover drum to free wheel when the cable reels are rotatably driven. [See U.S. Pat. Nos. 3,019,450 & 3,050,743, Lamb].
In clutch de-coupled systems of the type pioneered by Lamb, in order to prevent biasing of the cover as it winds around the cover drum during retraction and to assure that the cover winds compactly and uniformly around the drum, adjustable braking mechanisms are utilized to slow or resist rotation of the respective free wheeling take-up reels to provide the necessary tension in the cables for assuring that cover edges curl around the ends of the cover drum. Such braking mechanisms typically are adjustable for each take-up reel. Also, a braking system necessary to prevent the cable reels from freewheeling when the cover is retracting otherwise because the reel diameter decreases as the cables unwind, the reels over rotate entangling the cables, a phenomenon referred to backlash in fishing reels, and bird-nesting pool cover industry. Moreover, the resistance provided such braking systems is typically not sufficient to prevent unwinding of the cable reels when a heavy object falls on an extended cover, a circumstance that can cause the cover to partial retract (open) presenting a child drowning hazard.
In early automatic pool cover systems the rigid boom spanning the width of the pool holding the front edge of the cover above the water was typically supported by a pair of wheeled dollies rolling on the side edges of the pool. The cables moving within the "C" channels of the track along either side of the pool were either directly secured in some fashion to the rigid boom, [Foster, supra], or were indirectly secured to the ends of the boom via fabric interfaces referred to as gores. [See U.S. Pat. No. 4,001,900, Lamb].
Slider mechanisms have supplanted the use of wheeled dollies for supporting the rigid boom carrying the front edge of the cover. Typically, such slider mechanisms are coupled to the respective ends of the boom and have an edge adapted for capture and sliding within the same or different "C" channels of the extruded track in which the beaded side edge of the cover is captured and slides. [See U.S. Pat. No. 4,686,717, MacDonald et al & U.K. Pat. No. 2,072,006, Lee].
As pointed out and extensively discussed in Applicant's related U.S. Pat. No. 4,939,798, in systems where slider mechanisms support the rigid boom, it is very important to maintain the boom oriented squarely between the track channels, otherwise the sliders carrying the boom will jam in the track channels stopping extension or retraction of the cover.
Also, in related U.S. Pat. No. 4,939,798, the Applicant describes and claims slider mechanisms which couple steel cables to the lines incorporated into the respective beaded edges of the cover. The steel cables extend between the sliders and the take-up reels. [See FIGS. 12 & 12a; col. 15, 1.37-col. 16, 1.7and claims 44; and claims 47-49].